Objective—To determine whether a deficiency in
systemic or local (pars intermedia) antioxidant capacity
is associated with pituitary pars intermedia oxidative
stress and pituitary pars intermedia dysfunction
(PPID) in horses.
Sample Population—Blood samples from 20 horses
with PPID and 20 healthy client-owned horses,
archived paraffin-embedded adrenal gland and substantia
nigra tissues from 20 horses, and pituitary
gland tissue from 16 horses.
Procedures—Total glutathione, superoxide dismutase,
and glutathione peroxidase activities were
determined in RBCs. Accumulation of a systemic
marker of oxidative stress (3-nitrotyrosine) was
assessed in plasma and formalin-fixed, paraffinembedded
adrenal gland and substantia nigra tissues.
Local antioxidants (total and manganese
superoxide dismutase, glutathione peroxidase, and
total glutathione) were measured in pars intermedia
Results—No significant differences existed in systemic
antioxidant enzyme activity or accumulation of
3-nitrotyrosine between horses with PPID and control
horses. In pituitary gland tissues, glutathione peroxidase
activity was increased in horses with oxidative
stress, whereas total glutathione concentration and
superoxide dismutase activity remained unchanged.
There was an age-associated decrease in manganese
superoxide dismutase activity in the pars intermedia.
Conclusions and Clinical Relevance—There was
no evidence of systemic accumulation of oxidative
stress markers or deficiencies in antioxidant capacity
in horses with PPID, suggesting that these are
unlikely to be major predisposing factors in the
development of PPID. Manganese superoxide dismutase
activity in the pars intermedia decreased
significantly with increasing age. Role of an ageassociated
decrease in antioxidant capacity for the
pars intermedia in the development of PPID in horses
warrants further investigation. (Am J Vet Res
Objective—To determine the effects of chronic exposure
to excess dietary copper (Cu) on liver specimens
from rats and the effects of dietary selenium (Se) supplementation
in experimental Cu toxicosis.
Animals—60 weanling male Fischer 344 rats.
Procedure—Rats were randomly assigned to 4
groups of 15 rats each and fed 1 of the following 4
diets: high Cu (500 μg/g)/adequate Se (0.2 μg/g); high
Cu (500 μg/g)/supplemented Se (2 μg/g); adequate Cu
(18 μg/g)/adequate Se (0.2 μg/g); or, adequate Cu (18
μg/g)/supplemented Se (2 μg/g). Five rats per group
were euthanatized after 3, 6, and 12 months, and liver
specimens were obtained for histologic examination,
histochemistry, metal analysis by atomic absorption
spectrophotometry, measurement of glutathione peroxidase
activity, and assessment of lipid peroxidation,
using quantification of malondialdehyde (MDA) by the
thiobarbituric acid reaction.
Results—Hepatic Cu concentration was significantly
higher in rats fed high Cu diets (range, 9 to 18 μg/g of
tissue [wet weight]), compared with rats receiving
adequate Cu diets (4.0 to 5.7 μg/g of tissue). Rats fed
high-Cu diets for 3, 6, and 12 months had mild multifocal
hepatitis often surrounding necrotic foci.
However, an increase in hepatic MDA content, indicative
of lipid peroxidation, was not detected in these
rats. Development of morphologic changes was not
prevented by use of dietary Se supplementation.
Conclusion and Clinical Relevance—Long-term
exposure to excess dietary Cu caused mild hepatic
lesions in Fischer 344 rats. Dietary Se supplementation
did not prevent hepatic damage in rats with Cu
toxicosis. (Am J Vet Res 2001;62:1423–1427)
Objective—To investigate effects of sample handling,
storage, and collection time and season on plasma α-melanocyte-stimulating hormone (α-MSH) concentration
in healthy equids.
Animals—11 healthy Standardbreds and 13 healthy
Procedure—Plasma α-MSH concentration was measured
by use of radioimmunoassay. Effects of delayed
processing were accessed by comparing α-MSH concentrations
in plasma immediately separated with that of
plasma obtained from blood samples that were stored at
4oC for 8 or 48 hours before plasma was separated.
Effects of suboptimal handling were accessed by comparing
α-MSH concentrations in plasma immediately
stored at -80°C with plasma that was stored at 25°C for 24
hours, 4oC for 48 hours or 7 days, and –20°C for 30 days
prior to freezing at –80°C. Plasma α-MSH concentrations
were compared among blood samples collected at 8:00
AM, 12 noon, and 4:00 PM. Plasma α-MSH concentrations
were compared among blood samples collected in
January, March, April, June, September, and November
from horses and in September and May from ponies.
Results—Storage of blood samples at 4°C for 48
hours before plasma was separated and storage of
plasma samples at 4°C for 7 days prior to freezing at
–80°C resulted in significant decreases in plasma α-MSH concentrations. A significantly greater plasma α-MSH concentration was found in September in
ponies (11-fold) and horses (2-fold), compared with
plasma α-MSH concentrations in spring.
Conclusions and Clinical Relevance—Handling and
storage conditions minimally affected plasma α-MSH
concentrations. Seasonal variation in plasma α-MSH
concentrations must be considered when evaluating
pituitary pars intermedia dysfunction in equids. (Am J Vet Res 2004;65:1463–1468)
Objective—To evaluate concordance among veterinary
pathologists in the assessment of histologic findings
in the pars intermedia of pituitary gland sections
from aged horses with mild signs suggestive of pituitary
pars intermedia dysfunction (PPID).
Sample Population—10 pituitary glands from aged
Procedure—7 pathologists were provided with signalment,
clinical signs, and a single H&E-stained pituitary
gland section from 10 aged horses with mild
signs suggestive of PPID. Pathologists described histologic
findings for each section and stated whether
findings were consistent with PPID. Agreement
among pathologists and with antemortem diagnostic
test results was calculated.
Results—Overall, only fair agreement was found
among the pathologists as to which horses had histologic
findings consistent with disease (mean ± SE
kappa value, 0.34 ± 0.069). Interpretation of individual
sections varied, with minimal agreement (4 or 5/7
pathologists) for 5 of 10 sections evaluated.
Postmortem assessment was in agreement with an
antemortem endocrine diagnostic test result 79% of
Conclusions and Clinical Relevance—Validation of
antemortem diagnostic testing for PPID in horses
often relies on the results of postmortem histologic
evaluation. The lack of consensus in histologic interpretation
of pituitary glands from aged horses with
mild clinical signs in our study indicates that postmortem
histologic evaluation of pituitary glands is an
inappropriate standard in validation of antemortem
diagnostic tests for detection of early PPID. Caution
should be used when interpreting diagnostic test
results in horses in which early PPID is suspected.
(Am J Vet Res 2005;66:2055–2059)
To assess drug-drug interactions between cannabidiol (CBD) and phenobarbital (PB) when simultaneously administered to healthy dogs.
9 healthy, purpose bred Beagles.
A 3-phase prospective, randomized pharmacokinetic (PK) interaction study of CBD and PB was performed as follows: phase 1, CBD PK determination and evaluation of CBD tolerability by 3 single-dose CBD (5 mg/kg, 10 mg/kg, and 20 mg/kg) protocols followed by 2-week CBD dosing; phase 2, a single-dose, 3-way, crossover PK study of CBD (10 mg/kg), PB (4 mg/kg), or CBD (10 mg/kg) administration plus PB (4 mg/kg); and phase 3, evaluation of chronic PB (4 mg/kg, q 30 d) administration followed by single-dose CBD (10 mg/kg) PK study.
Although there were variations in CBD PK variables in dogs receiving CBD alone or in conjunction with PB, significance differences in CBD PK variables were not found. No significant difference was observed in PB PK variables of dogs receiving PB alone or with CBD. During chronic CBD administration, mild gastrointestinal signs were observed in 5 dogs. At daily CBD doses of 10 to 20 mg/kg/d, hypoxia was observed in 5 dogs and increased serum alkaline phosphatase (ALP) activities (range, 301 to 978 U/L) was observed in 4 dogs. A significant increase in ALP activity was observed with chronic administration of CBD during phase 1 between day 0 and day 14.
CONCLUSIONS AND CLINICAL RELEVANCE
No significant PK interactions were found between CBD and PB. Dose escalation of CBD or adjustment of PB in dogs is not recommended on the basis of findings of this study.